Reciprocating downhole pumps are used to elevate production fluids from a subterranean oil and gas well. Such pumps are typically driven by a motor, such as a pump jack, at the ground surface. A stationary standing valve is positioned at the bottom of a string of production tubing near the producing perforations of the well. A hollow cylindrical pump barrel is positioned above the standing valve and contains a traveling plunger with a traveling valve assembly. The plunger assembly is attached at its top end to a sucker rod which is actuated by the pump jack at the surface.
On the upstroke of the travelling plunger, the travelling valve assembly closes, so that each upstroke lifts a column of production fluid towards the surface. Meanwhile, the standing valve opens to charge the pump barrel below the travelling valve assembly with production fluid. On the downstroke of the travelling plunger, the travelling valve assembly opens to allow the production fluid to charge the pump barrel above the travelling valve assembly with a new column of production fluid for the next upstroke. Meanwhile, the standing valve closes to prevent the fluid drawn into the pump barrel below the plunger from flowing back into the production tubing.
The traveling valve assembly in such reciprocating pumps commonly consists of a ball and seat valve or a flapper valve. On the downstroke, the movement of the travelling valve assembly through the fluid and the incompressible nature of the liquid trapped between the traveling valve and the standing valve lifts the ball or the flapper from the valve seat thereby opening the valve. On the upstroke, the hydrostatic pressure of the fluid above the ball or the flapper, and the movement of the travelling valve assembly through the fluid forces the ball or flapper down onto the seat thereby closing the valve. Other types of valves employing similar actuating mechanisms on the up and downstrokes are employed, but in each instance, the consistent opening and closing of the traveling valve with the downstrokes and upstrokes of the plunger is essential to the efficient pumping of production fluid up the production tubing.
Although the reciprocating downhole pump described above is commonly used, there are circumstances that can render its use problematic and inefficient. For example, production fluids containing dissolved gases can result in an undesirable phenomenon known as “gas locking” if dissolved gases break out of solution. On the upstroke of the plunger, the gases flow upwards through the open standing valve into the pump barrel between the standing valve and the plunger. On the downstroke of the plunger, the plunger will compress the gases between the plunger and the closed standing valve. This is counterproductive to the effect of the production fluid in the pump barrel below the travelling valve forcing the valve member to its open position against the weight of the production fluid above the travelling valve. On the following upstroke, the compressed gas in the pump barrel between the traveling valve and the standing valve expands to fill the enlarged space. This prevents the upward flow of more production fluid from the production tubing through the standing valve and into the pump barrel. As such, the upstrokes and downstrokes of the pump simply result in the repeated compression and expansion of trapped gas between the standing valve and the traveling valve, and the pumping of fluid is prevented or decreased in efficiency. An associated problem is “fluid pounding” which occurs when the space in the pump barrel below the traveling valve is partially filled with fluid and partially with gas. The consequence of such a composition in the pump barrel is that the plunger forcefully enters the fluid level part way through the downstroke. This causes undesired vibrations, or “pounding”, through the production string leading to mechanical failure and expedited wear.
Therefore, there is a need in the art for a tool that helps to ensure that a traveling valve assembly of a reciprocating downhole pump opens and closes as intended.